This invention relates to solid-state compositions for use as gas sensors.
The composition Cr2xe2x88x92xTixO3+y with 0.005xe2x89xa6xxe2x89xa60.45, and where y is determined by the charge balance in the crystal lattice and the equilibrium of oxygen vacancies with oxygen gas in the ambient atmosphere, has been described as a gas sensitive resistor material having advantages of low sensitivity to relative humidity and high sensitivity to gases such as carbon monoxide. However, the effect of relative humidity change on this material is still too large to allow sensors manufactured using it to meet modern standards for carbon monoxide detectors for domestic use.
The present invention relates to compositions which have the advantage of an even lower sensitivity to relative humidity whilst retaining a high sensitivity to carbon monoxide.
The invention provides the following compositions:
binary oxides of the formula Cr2xe2x88x92xMxO3 with M=Fe or Mn and 0.005xe2x89xa6xxe2x89xa61.95.
Ternary oxides of the formula Cr2xe2x88x92x(M1zM21xe2x88x92z)xO3 with M1=Fe or Mn, M2=Fe, Mn or Al, 0.005xe2x89xa6xxe2x89xa61.95 and 0.005xe2x89xa6zxe2x89xa60.995;
ternary oxides of the formula Cr2xe2x88x92x(M1zM21xe2x88x92z)xO3 with M1=Fe or Mn, M2=Ti and 0.005xe2x89xa6xxe2x89xa61.95, 0.005xe2x89xa6zxe2x89xa60.45;
quaternary and quinternary oxides of the formula Cr2xe2x88x92x((M1aM2bM3c)zM41xe2x88x92z)xO3 with M1=Fe, M2=Mn, M3=Al and M4=Ti, and Oxe2x89xa6a,b,cxe2x89xa61, 0.005xe2x89xa6xxe2x89xa61.95, and 0.005xe2x89xa6zxe2x89xa60.45.
Within these compositions, a very wide range of impurities, specifically including alkali and alkaline earth metals and transition metals, can be tolerated without degradation of the properties.
The invention also provides gas sensors incorporating these inventive compositions.